On a Remote Island, Lessons In How Ecosystems Function

Transformed by British sailors in the 19th century, Ascension Island in the South Atlantic has a unique tropical forest consisting almost entirely of alien species. Scientists say that what has happened there challenges some basic assumptions about ecosystems and evolution. By fred pearce

I was standing on the summit of an extinct volcano in the center of one of the most remote islands on the planet: Ascension Island in the tropical South Atlantic. Midway between Brazil and Africa, Ascension is a thousand miles from the nearest speck of land. Below me was a harsh treeless moonscape of volcanic clinker, baking in the sun. But in the cool mountain air, 800 meters up, I was surrounded by lush greenery and a light mist from a cloud settled over the mountaintop.

They call it Green Mountain. But the greenery is new. My guide, the island’s conservation development officer, Stedson Stroud, peered around us and

Ecologists Daniel Simberloff, of the University of Tennessee, and Donald Strong, of the University of California, Davis, have written a critical appraisal of Fred Pearce's analysis of what has occurred on Ascension Island. Read their critique. READ MORE

smiled. “Nothing you see here is native,” he said. “Except for a few ferns, everything has been introduced in the past 200 years.”

On our way up the mountain, we had walked through New Zealand flax, Bermuda cedar, Chinese ginger, South African yews, guava from Brazil, European blackberries, and screw pines that grow higher here than they do at home on the islands of the Pacific. The summit, improbably covered in a dense stand of Asian bamboo, rattled like a huge wind chime in the brisk trade winds. All this had been introduced by the British Navy during the early- and mid-19th century, along with rabbits, cats, donkeys, hedgehogs, mynah birds, bees, and much else.

The forest that covers Green Mountain is said to be the only tropical forest in the world — apart from monoculture plantations — that is entirely man-made. It is an ecosystem, but like no other. Stroud admitted that, as a

The success of the forest on Green Mountain is creating controversy among ecologists.

conservationist and member of the International Union for Conservation of Nature’s Species Survival Commission group for the South Atlantic, he should perhaps be rooting out all those alien species. But if he did, there would be almost nothing left. And in any case, he mused, he is presiding over something profoundly interesting — a functioning ecosystem in which a ragbag of species shipped in from all over the world thrive as if they had been together for millennia.

Though badly under-researched because of the island’s remoteness, Green Mountain is being hailed as the icon for a fundamental reassessment of many nostrums of both environmentalist and ecological science. It is also creating controversy among ecologists. What are we to make of this confected cloud forest? Is it nature or a garden? Is it a beacon for re-greening the planet or a biological abomination?

Ascension Island, which is just under twice the size of Manhattan, erupted from the Atlantic floor a million years ago. The last new lava flows were 700 years ago. The island has been in British hands for almost 200 years, as a base for controlling the Atlantic. These days, the island is peppered with aerials that track orbiting spacecraft, communicate with nuclear submarines, and listen in secretly on satellite-relayed communications. The electronic spies of Britain’s GCHQ, and possibly also the NSA, are here.

It also has one of the longest airstrips in the world. Built by the U.S. Army during World War II on land leased from Britain, it provides a secure stopping point for U.S. military flights into Africa. When I arrived on a British flight in early July, no fewer that nine large U.S. military aircraft were sitting on the tarmac, all busy protecting President Obama during his visit to Africa.

Inevitably, such human traffic brings alien species. Some lava flows and cinder cones are now covered in fast-spreading tobacco plants and Mexican thorns, whose seeds are eaten and distributed by feral donkeys and sheep. They are accidental introductions. But what sits on Green Mountain is largely deliberate.

A view from Green Mountain, located in the South Atlantic 1,000 miles from Africa.

When Charles Darwin visited Ascension Island aboard the Beagle in 1836, he complained about Ascension’s “naked hideousness.” But the Royal Navy garrison, established in 1815, set about changing that. First, it put together a farm on the few patches of natural soil on the mountain.
Then British colonial botanist Sir Joseph Hooker — a future head of the famous botanical gardens at Kew in London who visited the island in 1843 — came up with the idea of growing trees to green the arid island and increase its rainfall. The idea was that the new vegetation on the mountaintop would scavenge moisture from the passing clouds. Further down the slopes, planting would encourage soil growth. Hooker’s ambition was nothing less than “terra-forming” the volcanic island, says Stroud in a recent paper with David Catling of the University of Washington, Seattle.

Today, the island has about 300 introduced species of plants to add to its 25 native species, says David Wilkinson of Liverpool John Moores University in the UK. Many are spreading. Above about 660 meters, Green Mountain is completely vegetated, with coffee bushes, vines, monkey puzzle trees, jacaranda, juniper, bananas, buddleia, Japanese cherry trees, palm trees, clerodendrum, green aloe and the pretty pink flowers of the Madagascan periwinkles. And Stroud says the vegetation captures more cloud moisture, just as Hooker had hoped, even though rainfall has declined in the lowlands around.

The invasion has been double-edged. The invaders have damaged some of the handful of endemic species that had found a foothold on the island

Plants gathered from across the world “self-organized by the mechanism of ecological fitting,” says a scientist.

during its million-year. Three of the endemic ferns are believed now extinct. But as we stood on the mountain, gazing south over an abandoned NASA tracking station, Stroud pointed out below us the spot where, in 2009, he rediscovered on a cliff face a single specimen of a species believed lost, Anogramma ascensionis. Now it is being propagated in the UK ready for a reintroduction.

In fact, many of the endemics seem to get on remarkably well with the motley collection of invaders, says Stroud. The ferns that once clung to the bare mountainside now prosper on the branches of introduced trees like bamboo. Stroud showed me ferns that he believes now thrive only on the mosses that grow on such branches.

Likewise, the profusion of Ascension land crabs — the island’s largest native land animals — that now feast on the fruits of alien trees like the guava. The only researcher to have studied the land crabs in recent times, Richard Hartnoll of the University of Liverpool, says that the invasive vegetation “increases the area of shade and shelter for crabs, and also provides a large resource of food” — perhaps replacing their former scavenging on seabird colonies.

You might think that this snugness would be of huge ecological interest? Yet, until now, visiting scientists have ignored it, says Stroud. Most researchers who make the long journey — the only practical way in is aboard a British military flight — have concentrated on the island’s charismatic populations of seabirds, green turtles, and the handful of endangered ferns.

Conservation officer Stedson Stroud says that nearly all plants on Green Mountain are not native to the island.

This blindness in research extends to conservation, says Wilkinson. The British government’s environmental policy for the island is the “control and eradication of invasive species” in order to “ensure the protection and restoration of key habitats.” (A major exercise to eradicate feral cats has been implemented under this policy.) But the policy has nothing to say about the protection of — or even ecological research into — the extraordinary novel ecosystem in their midst on which the indigenous species often depend.

That is a shame. For, according to an increasing number of ecologists, the unique ecosystem on Green Mountain may hold important lessons about how ecosystems around the world function. In the growing scientific literature over the past decade about “novel” ecosystems, in which human agency or interference is a central factor in their makeup, Green Mountain is one of the most cited examples. More than that, the mountain’s ecosystem calls into question a series of widely held assumptions about how complex, biodiverse ecosystems evolve — or indeed whether they evolve at all.

According to mainstream ecological theory, this cloud forest really should not exist. Certainly it should not thrive. Complex forests ecosystems are believed to take millions of years to develop, as each species evolves to fill its own niche in the system, creating a perfected “climax” ecosystem. But Green Mountain doesn’t fit that paradigm. It just seemed to happen according to the chance introductions of British sailors.

As Stroud and Catling wrote, species on Green Mountain “have bucked the standard theory that complexity emerges only through co-evolution.” On Ascension, plants gathered from across the world “self-organized by the

This forest suggests that even highly biodiverse ecosystems may be accidental, temporary, and versatile.

mechanism of ecological fitting,” says Thomas Jones of the U.S. Department of Agriculture in Logan, Utah.

Not everyone agrees. Alan Gray, an ecologist at the University of Edinburgh in Scotland, suggests that some species that washed up on Ascension may have known each other before. “There would appear to be a high likelihood of importing already established coevolutionary relationships,” such as moths and other invertebrates arriving with the trees in which they have evolved to lay their eggs, he says. According to Stroud, there has been no systematic study of invertebrates to unravel this conundrum.

Nonetheless, Wilkinson argues that the accidental cloud forest suggests strongly that even highly biodiverse ecosystems may often be accidental, temporary, and versatile.

Whatever the truth, the stakes are high for ecologists. But while the ideas about ecological fitting go against the grain of mainstream thinking among environmentalists, they are not out of line with the teachings of Charles Darwin. Some see co-evolution and the creation of perfected ecosystems of native species as the ecological flowering of Darwin’s thinking on evolution. But the evolutionary biologist Stephen Jay Gould has been among those who disagree strongly.

In an essay published in 1998, he attacked the “romanticism” of ecologists who sought to protect native plants against invasive species. He said their idea that Darwinian evolution created collections of species that were perfectly evolved to work together, like cogs in a machine, was false. “The Darwinian mechanism includes no concept of general progress or of optimization,” Gould wrote. In fact, Darwin never said it did. Most of the time, species simply fitted in as best they could. “Survival of the fittest” was just that.

New research shows that humans have been transforming the earth and its ecosystems for millenniums — far longer than previously believed. These findings, Fred Pearce writes, call into question our notions about what is unspoiled nature and what should be preserved.READ MORE

Whatever the theoretical implications of the forest on Green Mountain, there are practical implications for conservationists, too. Harvard University ecologist E. O. Wilson has said that the 21st century will be the century of ecological restoration. And Green Mountain suggests that restoration could be much easier than many believe. Ecologists may not have to painstakingly reassemble the complex ecosystems that have been lost. They often may be able to let nature take its course.

As Wilkinson put it: “Is it possible... to suggest, for example, that large deforested areas of Amazonia could be returned to functioning forest on a 100-year time-scale?” And maybe not just former rainforests. If a forest can form so quickly and successfully on a volcano in the middle of the Atlantic, they why not in other unlikely places?

As Catling and Stroud note, “Green Mountain might help inform strategies to green some deserts or other barren locations in the world.”

COMMENTS

Coevolution exists. Distance exists. Ecosystems contain many parts that would be superfluous if the world were made of one giant supercontinent. But it's not. There are functional losses to ecosystems from species eradications and extinctions. There are many examples of this, e.g., European honeybees in the Americas. Their history of introduction, ascendancy and demise is a good illustration of this.

Posted by
Andy
on 26 Aug 2013

Thank you for this excellent article about the value of “novel ecosystems,” the term now used to describe an ecosystem composed of both native and introduced species. There is similar research conducted by Ariel Lugo in Puerto Rico and Joe Mascaro in Hawaii that reached the same conclusions.

Introduced species are increasing biodiversity, not reducing it. Introduced tree species are performing the same ecological functions as native species, such as carbon sequestration and nutrient cycling. And in many cases, introduced species are actually benefiting native species. On Hawaii, for example, introduced tree species capable of nitrogen fixing are transforming barren volcanic soil to soil capable of supporting native species. The work of these two scientists is described here: http://milliontrees.me/2012/11/20/ecosystem-processes-are-comparable-in-native-and-non-native-forests-in-hawaii/

The assumptions of invasion biology are quickly losing ground amongst scientists. Unfortunately, careers were built on those assumptions, so they are not easily abandoned. And a restoration “industry” has developed economic interests in the huge eradication projects that are based on the mistaken assumption that merely eradicating non-native species will result in the return of the natives. Those who watch those projects know that is largely a fantasy unless a commitment is made to intensive gardening in perpetuity.

Yale Environment 360 has put another nail in the coffin of nativism. Thanks!

Posted by
Million Trees
on 26 Aug 2013

"Introduced species are increasing biodiversity, not reducing it."

That statement ignores scale. If you trade local diversity increases (due to addition of non-natives) for regional or global species losses (again due to the non-natives) is that really a good thing?

I agree that many assumptions of invasion biology should be challenged, but doing nothing in the face of invasive species will inevitably lead to extirpation or extinctions.

Posted by
Tony
on 26 Aug 2013

Would the author please give references for the following statements,

"The success of the forest on Green Mountain is creating controversy among ecologists."

"According to mainstream ecological theory, this cloud forest really should not exist."

"Complex forests ecosystems are believed to take millions of years to develop, as each species evolves to fill its own niche in the system, creating a perfected “climax” ecosystem."

"ecological fitting"..."it holds that ecosystems are typically much more random."

Much more random than what?

Posted by
Donald Strong
on 28 Aug 2013

Did the introduction of cheat grass increase the diversity of western U.S. sagebrush communities? Did the introduction of Dutch Elm, Chestnut Blight, Emerald Ash Borers, and Butternut Decline increase the diversity of U.S. deciduous forests? Did the introducton of honeybees increase the diversity of native pollinators in the SW U.S.? Did introduction of the brown tree snake increase the number of birds foun on Guam?

The answer to all of the above is no.

Many introductions have been scientifically documented (null hypothesis rejected) to reduce plant and animal diversity. Non-native species introduction is the most often cited reason, second only to habitat loss, of species extinction or near extinction as documented by the U.S. Fish and Wildlife Service.

The example of honeybee introduction to N. America is an especially good example as there were not only extinctions of native pollinators, but functional loss of pollination services and subsequent plant losses as well. The bees not only displaced native pollinators, they decreased the amount of the warm season when pollination was occurring as well as time of day. In other words, they didn't replace or enhance the pollinator function of the native ecosystem. And to make matters worse, now that their native pathogens and parasites have caught up with them, they are declining precipitously which presents an even greater threat to the ecosystem's pollination function.

Posted by
Andy
on 28 Aug 2013

It seems obvious to me that 'ecological fitting' would be a key mechanism of 'co-evolution.'

There must be something about this that I'm missing?

Posted by
Steve
on 28 Aug 2013

Amen, Andy.

I think you've oversimplified this one, Fred. By framing the Green Mountain story as part of a two-options debate — one side wrong, the other right — you've left no room for the way invasion and system change really happen, i.e., a mix of outcomes, favoring some species (native and alien) and some ecosystem services, disfavoring others, and setting in motion further adaptations that can't be easily predicted.

Posted by
Alan
on 29 Aug 2013

After thinking about Pearce's writing a bit, I have come to the conclusion that a public discussion of it is worthwhile. As a seed, I offer, "Pearce's writing is a version of that of Bjorn Lomborg. Neither takes seriously the topic. Both begin from a political or cultural perspective and employ rhetoric that short circuits substantial consideration of the topic." Why is someone like this on e360?

Posted by
Donald Strong
on 29 Aug 2013

Uncle Fred is a member of the new school of thought that advocates for the abandonment of the defense of native biodiversity. The fact that Yale e360 gives such fringe thinkers column space is evidence of a problem with the editorial staff's understanding of basic ecology. Leopold et al. would be most disappointed.

Posted by
Halifax
on 29 Aug 2013

Life takes hold where it can. How long does an invasive species have to be there before it becomes the norm? Leave those feral cats alone.

Posted by
Jamie
on 29 Aug 2013

This article is a poster child for poor scientific journalism.

"Yet, until now visiting scientists have ignored it, says Stroud," referring to the neobiotic assemblage on Green Mountain.

The author and those quoted seem to be ignorant of the decade old neutral theory of ecology of Hubbell et al, that many assemblages do assemble randomly, even in tropical forests that are touted to be highly co-evolved. Islands with depauparate floras often end up with random assemblages as there are 'empty' niches galore and alien species may displace natives. Here in Hawaii that has happened such that most lowland valleys are their own random little communities. Wilkinson also seems unaware that the first peoples of the Amazon modified it extensively and it "recovered" on its own after the Spanish arrived to what he and others call a "functioning" forest, an operationally useless term.

Also, those interested might care to read "The Terrestrial Ecology of Ascension Island," Journal of Applied Ecology, Vol. 1, No. 2 (Nov., 1964), pp. 219-251. It is 50 years old and still has something to teach us about Ascension.

As a thought experiment, apply these arguments to infectious disease and to indigenous peoples.

Eric Duffey

Posted by
David Duffy
on 29 Aug 2013

Several comments in this article betray that the writer is either a) strikingly naive about the last several decades of thinking and research on assembly of ecological communities, or b) taking a good deal of license to set up a false tension for journalistic 'flare.'

Take this quote, for example: "According to mainstream ecological theory, this cloud forest really should not exist ... Complex forest ecosystems are believed to take millions of years to develop, ... creating a perfected 'climax' ecosystem."

"Climax" theory has not been the prevailing paradigm for decades, and few community ecologists would start with the assumption that any ecological community is a tightly integrated, coevolved, stable system. If it took millions of years of coevolution in a stable species pool to develop a "complex forest ecosystem," all landscapes that were glaciated 20,000 years ago (much of Europe and temperate North America, for example) would be disqualified — an absurd notion.

To the comments and references of other ecologists above, I would add the last 50 years of work by paleoecologists as convincingly demonstrating that communities are continuously in flux, reassembling, plastic. Novel communities are not infrequent — you don't have to go to remote islands to find them. But, yes, they're interesting...

Posted by
Kerry Woods
on 29 Aug 2013

Mr. Pearce writes that "many of the endemics seem to get on remarkably well." Yet 30 percent of the known endemics are extinct, 10 percent are listed as critically endangered by the IUCN, and the remaining 60 percent are classified as threatened. There are few places in the world whose endemic species have been so thoroughly decimated. Were he reporting on England, rather than spinning a romanticized story about England's colony, one suspects Mr. Pearce would be rather more concerned that 100 percent of his island's endemic species are extinct, endangered, or threatened.

He misleadingly quotes a government document out of context to suggest the policy is to remove all exotic species. That is not and never has been government policy. Only a tiny portion of the 300+ exotic species are targeted for control, in every case to prevent the extinction of the endemic species Pearce dismisses as a "handful of endangered ferns." Given Pearce's apparent disinterest in the past and threatened extinction of the island's endemic species, I'm not surprised that he objects to exactly those efforts instituted to save them, but he should at least correctly describe the scope and intent of the work.

Finally, it is just ridiculous to assert that, "According to mainstream ecological theory, this cloud forest really should not exist." There is no ecological theory, mainstream or otherwise, that predicts that introduced species, in principle, cannot ecologically interact with other species over long periods of time given the right conditions. If this were the case, there would be no concern about invasive species. No ecologist, moreover, would gainsay that any group of species placed together (such as on Ascension Island) will proceed to interact such that those which cannot survive the interaction will disappear and those that can will remain. This is exactly what happened on Ascension. Native and introduced species which could not survive the interactions disappeared or retreated to isolated areas where the interactions were reduced. Those that which could thrived and spread.

Mr. Pearce's highly romantic portrayal of the ecological status of Ascension Island requires him to ignore the devastation wrought on the endemic species by the massive introduction of non-natives and to imagine that he has discovered an exciting, new, unorthodox theory and habitat which he can champion against a fictitious "mainstream" establishment. This would be merely fatuous if there were not such a long history of colonizers dismissing the damage they wrought on their colonies with romantic notions of having "improved" them. Within that historical context, Mr. Pearce's essay is rather more disturbing.

Kieran Suckling
Executive Director
Center for Biological Diversity

Posted by
Kieran Suckling
on 30 Aug 2013

"Functioning" as a standard for judging an ecosystem's condition is meaningless, but more often, as here used by Pearce, dangerous.

By definition, every ecosystem is always functioning, regardless of how degraded it might be or how many species have gone extinct. Ecosystems don't cease to function and die, like individuals. They change. The processes and species that exist at each point in the change are "functioning": they use each other for food and shelter, they are born, grow and die, they respond to climate, weather and disturbance, etc. This continued "functioning" tells us absolutely nothing about its ecological state and conservation value.

The primary conservation work at Ascension has been to stem the tide of extinction sweeping away the endemic species. To extol, in the midst of this catastrophe, that the forests are "functioning" passes beyond the meaningless to the pernicious. It offers up a non-conservation standard that allows virtually any action while pretending that it is a meaningful standard.

The same confusion reigns in Pearce's strange use of the term "restoration." Type conversion of one ecosystem to another — as happened at Ascension — is not "restoration" in any possible sense of the word.

Functioning and restoration are just buzz words in this kind of confused journalism to indicate positivity. That might be fine for new age, self-help discussion group, but is unacceptable in a political/ecological forum where we need to clearly understand what we're talking about and make hard judgments about policy.

Posted by
Steve
on 30 Aug 2013

This essay misrepresents Stephen J. Gould.

Dealing admirably with the thorny issue of plant introductions, nativeness and migration, Gould notes that one good reason to control invasive plants is they can cause the extinction of native plants. Pearce leaves out that cautionary note, giving the false impression that Gould was opposed to all control of invasives. The omission is mysterious given that the central invasive control effort on Ascension Island is to prevent the extinction of native species.

Other commentators have noted Pearce's downplaying, even disinterest, in the extinction of Ascension Island species. Perhaps that disinterest is at the heart of this essay's problems. Extinction, like racism and sexism, is a fundamental ethical issue. If that ethical awareness is missing, it can be hard to comprehend why ecologists and conservationists do what they do.

Posted by
Ben
on 30 Aug 2013

Interesting and thought-provoking article. I fully believe that nature can do a good job when left to its own devices after such introductions. Still, that does not mean that a "man-introduced-nature-constructed" ecosystem should be preferred over the pre-human condition. Maybe restoring Ascension Island is not worth the cost (given other priorities), and could be profitably studied as to how invasives and natives interact, but we should not be sanguine and accept such conditions as the "new normal." With apologies to Darwin, who seemed to under-appreciate the place, that was its "native state" and nature needs to be celebrated — the good, the bad, and the ugly.

Posted by
E. Taylor
on 31 Aug 2013

Also, the desert doesn't need to be "greened." It's supposed to be a desert. These ecosystems are already remarkably diverse and adapted to uniquely difficult conditions. What an incredibly arrogant and ignorant comment.

Posted by
Charlie
on 02 Sep 2013

This is a comment on the "Counterpoint" of Professors Strong and Simberloff, which does not take comments:

This debate illustrates an important point. There is an enormous gap between the science of invasion biology and its practical application in the thousands of “restorations” that are taking place all over the world. Professors Simberloff and Strong are speaking for the former, and Mr. Pearce’s article is based on his accurate observations of actual projects. As a member of the public, my interest is in the latter because of the damage that is being done to the environment under the vague promise of “restoration.”

Mr. Strong is the creator of the project that is eradicating all non-native Spartina marsh grass on the entire West Coast of the United States. He is therefore in a position to at least be aware of the consequences of that project. The eradication of non-native Spartina has decimated the population of the endangered clapper rail in the San Francisco Bay because it provides year-around superior cover compared to native Spartina. One would think that the Endangered Species Act would trump the Spartina eradication project on behalf of the clapper rail, but it has not. This is an illustration that those who object to these destructive projects are not just interested in serving humans, as Strong and Simberloff claim.

The Spartina eradication project is spraying imazapyr on our coastal marshes in alarming quantities, often using aerial applications from helicopters. Imazapyr is a relatively new pesticide about which little is known. For example, no tests have been conducted on the impact of that pesticide on shore birds. One would think that such tests would be a prerequisite to these projects, but they are apparently not. The few tests that are required by law tell us that imazapyr is very mobile in the soil and does not dissipate quickly. The ultimate damage that we are doing to our coastlines is yet to be known.

Secondly, Strong and Simberloff claim that restorationists are not attempting to replicate historical landscapes. They are mistaken in that assumption. Many native plant “restorations” are doing just that. The most conspicuous examples are grassland restoration projects taking place all over the country, especially in the Midwest. These projects are the poster child for the public’s negative reaction to these projects.

Grassland prairie was largely an artifact of the hunting practices of Native Americans. They set fire to the grassland often enough to prevent natural succession to shrubland and subsequently forest where soil and climate conditions support trees. Restorationists are attempting to return shrubland and woodland to grassland in order to replicate the pre-European landscape that was not natural. These projects require the destruction of shrubs and trees, many of which are natives. Herbicides and prescribed fire are used to destroy the unwanted vegetation and they must be used in perpetuity to prevent that artificial landscape from succeeding to shrubs and trees. These projects are not the “evolutionary trajectory” of grassland, as Strong and Simberloff claim. The public reacts to the use of herbicides as well as the prescribed burns which pollute the air and endanger residential communities.

Academic careers have been built on the hypotheses of invasion biology. Academics who subscribe to those hypotheses would be wise to think carefully about how invasion biology is used by its practitioners and to understand that the public is little interested in the science if their public lands are being destroyed and their environment damaged.

Posted by
Million Trees
on 11 Sep 2013

Also in response to Simberloff and Strong: These ecologists started off their essay with a highly defensive, name-calling tone, immediately revealing their bias.

As they continued with a more reasoned argumentation, that impression for me was solidified. In effect, Pearce points out how many exotic species together can produce complexity and, at least in the short term, stability. That point Simberloff and Strong did not want to acknowledge as it apparently threatens their own way of conceiving restoration.

They tried to critique Pearce by criticizing his lack of precision in terminology, a position that scientists rightfully must hold in a scientific paper, but in a popular science magazine has much less validity as terms need to be more metaphorical and authors and editors have less space and audience patience to achieve scientific precision. In any event the two authors merely qualified and conditioned what Pearce stated, they did not dethrone the co-fitting that seems to be occurring.

I agree with the authors that what we see on Ascension Island may not have such high applicability to the field of restoration, perhaps only in situations of recovery after complete devastation.

In summary, I applaud Peace for thinking outside the box and of course anytime anyone does that in any field, he or she is bound to be criticized by those who feel threatened, whether the thinker is right or not.

Posted by
Jon Kohl
on 12 Sep 2013

Many of the comments opposing Fred Pearce's views (and more interestingly, those suggesting he should have been muzzled) tacitly take nativeness to be an ecological or evolutionary 'good' that human agency diminishes or destroys. But biotic nativeness is at best a weak, archaic theoretical construction, and at worst a nostalgic sentiment (see http://www.academia.edu/462808/The_Rise_and_Fall_of_Biotic_Nativeness_A_Historical_Perspective ).

Those who hold that species introductions reduce biodiversity rest their claims on an exoticist wish that different places should support different taxa, even while willingly and correctly pointing out that certain biomes (such as the "Mediterranean") occur in various far-flung places around the planet. Indeed, if it were not the case that suites of prevailing conditions often repeat themselves, introducing species from one place to another would necessarily fail. That they do not repeat themselves precisely means that introduced populations immediately encounter different "selective pressures" from those in the source population, so the gene frequencies of introduced populations immediately begin to vary from their progenitors -- that is, they follow a different evolutionary trajectory — that at some point entails speciation. This can happen in surprising ways, including hybridization with native or other introduced congeners. This is dismissed as damaging introgression by nativists, but only if a human hand is detectable somewhere in the dispersal chain. Speciation by any process undeniably increases global biodiversity unless we redefine biodiversity to exclude the outcomes of particular kinds of human agency. In the face of evolutionary change, recent moves in redefining nativeness have included declaring any successors of an introduced population, regardless of evolutionary drift or innovation, to be permanently, irrevocably alien and (again) declaring only native species to count as biodiversity — even on Ascension Island.

It is worth pointing out that Kieran Suckling's Center for Biological Diversity is more pragmatic about introduced species than his comment suggests. The organization is avidly resisting release of beetles to defoliate introduced Tamarix in the southwestern US (because a listed endangered 'native' bird has just as avidly adopted the alien plant as nesting habitat within its critical range — see http://www.biologicaldiversity.org/news/press_releases/2013/southwestern-willow-flycatcher-03-07-2013.html).

The fact is, modern humans are significant dispersers of biota. Despite the seeming geological suddenness of this development, it is not self-evident from the point of view of the dispersed species that such dispersal is a bad thing — even though, in contrast to the ubiquitous hitchhiker/stowaway metaphor they have actually been abducted and cast away, to sink or swim wherever they land. After all, very few introduced species can be aware in any sense that they don't belong where they are, or even that there is anywhere else to be.

Persistence is evidence of belonging. The persistence of one population may tip the balance against the persistence of other populations, even longstanding ones, but it was ever thus. Even Charles Elton (in 1930!) declared "the balance of nature does not exist, and perhaps never has existed." Despite the sincere efforts of restorationists, putting Humpty Dumpty together again is a low percentage game, and success is only as complete as our knowledge of 'initial conditions,' and only holds until the next introduction unless we continually intervene on the outcomes of our interventions. There are a lot of people on this planet, but not enough, I suspect, to garden it back to whatever we might agree constitutes a natural state.

Posted by
Matt Chew
on 15 Sep 2013

Matt Chew's argument that "it is not self-evident from the point of view of the dispersed species that such dispersal is a bad thing" is true, but bizarrely missing all ethical content. The colonization of America was not seen as "a bad thing" by the Europeans, but was genocidally deadly to Native Americans. China's colonization of Tibet is looked on favorably by the Chinese government, but not so favorably by Tibetans. Should we ignore the destruction of Native American and Tibetan cultures because the colonizers accrued a benefit from it?

The introduction of new species to Ascension Island drove a third of the island's endemics extinct. The remaining 70 percent are all endangered, with one being reduced to a single plant in the wild. I can't imagine any ethical world view which would not find that a bad thing.

The only way to justify the mass extinctions caused by human introduced species is to deny we have an ethical responsibility not to wipe out other species, just as at one point in time Europeans denied we had any ethical responsibility toward Native Americans and China currently denies an ethical responsibility toward Tibetan sovereignty.

We have a responsibility to respect the lives, freedom and equality of other people, other races, other genders, other sexual orientations, and other species. It is as simple as that.

Professor Chew, like so many others who should know better, equates "biodiversity" with species diversity. It cannot be said too often, biodiversity is not simply shorthand for species numbers. It comprises the full range of diversity, from genes to species to associations to ecoregions, and all their interactions.

And of course Elton understood, "the balance of nature does not exist, and perhaps never has existed," as did Clements and Leopold and any number of naturalists who have spent time in the field, if by balance of nature is meant a static arrangement of fixed entities. This does not negate a particular integrity to evolve from the interactions of native species and ecosystems — an integrity which, when measured against the vagaries of human history, offers an order of relative wholeness.

It is this wholeness, Leopold's "land health," that, in part, confers upon wild nature its ethical bearing. This bearing challenges Pearce and the so called "environmental modernists," and their view in which nature is valued for the "ecosystem services" it provides to people; the lands and waters invaded by non-native species are "novel ecosystems;" and the idea of wilderness is a "nostalgic sentiment" we just need to get over.

Posted by
Tim Hogan
on 23 Sep 2013

From the ivory tower, we are asked to consider the “integrity” of ecosystems and their “ethical bearing.”

Once again, from the real-world, where we watch the application of invasion biology on the ground, we ask: How does an urban park being sprayed with toxic pesticides have integrity or ethical bearing? In an urban park in which 90 percent of all the plants are non-native, how does eradicating all the non-native plants result in more biodiversity, whether defined as genetic diversity or by any other measure?

While academics quibble over these theoretical questions, the practical application of their work is damaging our public open spaces. No one in the ivory tower is willing to address this real-world concern.

By the way, can anyone tell me that Aldo Leopold promoted the use of pesticides?

Posted by
Million Trees
on 24 Sep 2013

Fred Pearce is expressing in a scientific way what I always felt deep down instinctively as a committed conservationist. I believe some scientists in their ivory tower have completely lost any common sense. I remember the story of Campbell Island where New Zealanders eradicated feral cats. After that, the vegetation, which was thriving when cats were there, decreased. There was in fact a complex interaction between cats, the local vegetation, and birds. And surprisingly bird life didn't increase after the eradication of the felines.

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